With a view to obviating the need for wired cabling connections between stations in local area networks (LANs), wireless local area networks have been developed and are now commercially available. However, the coverage area of wireless LANs is restricted especially in an indoor environment, due to the presence of structural features such as walls and floors in buildings, for example. Also, it may be desirable for stations in a wireless LAN to communicate with remote facilities or resources such as servers. Therefore, it has been proposed to connect the wireless LAN via interface devices to a backbone LAN such as a wired LAN, which can be connected to the remote facilities and/or other wireless LANs.
Furthermore, where a mobile wireless station, such as a portable data processing unit provided with a wireless transceiver, for example, moves around it may move in and out of the range of various interface devices connected to the backbone LAN. It is therefore necessary for the backbone LAN to be kept up-to-date as the location of the mobile wireless station, in particular, which interface device is currently in communication with the mobile wireless station.
European Patent Application No. 0,483,544 discloses a wireless communications network including a plurality of mobile data stations in bi-directional communication with header stations which are connected into a wired LAN and which define communication cells. If a mobile data station crosses over from one cell to another, the mobile station determines a new header station for communications access to the wired LAN. The base stations periodically transmit broadcast messages identifying the base station and the loading factors at the base station. Using these messages a mobile station will determine all header stations that are potential owners of the mobile station and maintain in memory a list of potential owner stations. If the current owner station remains a potential owner, and the signal strength of the current owner station is acceptable, then the current owner is retained. Otherwise, the mobile station determines a new header station based on the loading factors of the potential owner stations, and, if the loading factors are equal, the signal strengths of the signals received at the mobile station. The header stations maintain routing tables. When a mobile station determines a new header station as owner, it transmits an uplink message to the new owner. The new header station determines if the mobile station has crossed a cell boundary, that is, the mobile station has a previous, different owner. If so, the new header station sends a message over the wired LAN to the previous owner, which then disowns the identified mobile station. This is a complex procedure.
International Patent Application No. WO 92/19059 discloses a system which includes a cable-based network to which are attached controllers which maintain a portable device in communication with the network for data transfer. The portable unit is registered with a controller by a process which involves transmitting a packet from the portable unit requesting a response from controllers, transmitting a response packet from each controller receiving the request, selecting one of the responding controllers at the portable unit according to criteria that enhance data transfer, and transmitting from the portable unit a packet identifying the selected controller to complete registration. The selected controller transmits a packet confirming the registration to the others via the network cable. The controller with which the portable unit was previously registered responds by de-registering the unit and transmitting any stored packets addressed to the unit via the cable to the newly selected controller. This procedure is also complex.